U.S. Pat. No. 8,729,571 discloses a conventional Fresnel lens that is used in a flashlight of a camera. Two such Fresnel lenses can be respectively disposed on two LED chips to guide light emitted from the LED chips to a pre-determined position. Since the thickness of the Fresnel lens is relatively thin, the Fresnel lens is suitable for portable electronic devices, such as mobile phones or laptops.
Since the abovementioned Fresnel lens is cut based on a convex lens surface, the optical properties of the abovementioned Fresnel lens is the same as a convex lens. Therefore, the conventional Fresnel lens can only convert the light emitted from the LED chips to a specific area. As a result, the light shape after the light passes through the Fresnel lens is very simple, the angle of the light is unlikely to be effectively changed, and the light emitted from the LED chips cannot be effectively and uniformly mixed. Moreover, since each LED chip is a surface light source, the conventional Fresnel lens may not effectively guide all of the light beams emitted from the LED chips to a pre-determined position. That is to say, loss of light is unavoidable.